Fluid catalytic cracking process and apparatus for maximizing light olefin yield and other applications

ABSTRACT

Apparatus and processes herein provide for converting hydrocarbon feeds to light olefins and other hydrocarbons. The processes and apparatus include, in some embodiments, feeding a hydrocarbon, a first catalyst and a second catalyst to a reactor, wherein the first catalyst has a smaller average particle size and is less dense than the second catalyst. A first portion of the second catalyst may be recovered as a bottoms product from the reactor, and a cracked hydrocarbon effluent, a second portion of the second catalyst, and the first catalyst may be recovered as an overhead product from the reactor. The second portion of the second catalyst may be separated from the overhead product, providing a first stream comprising the first catalyst and the hydrocarbon effluent and a second stream comprising the separated second catalyst, allowing return of the separated second catalyst in the second stream to the reactor.

FIELD OF THE DISCLOSURE

Embodiments herein generally relate to systems and processes forenhancing the productivity and/or flexibility of mixed catalyst systems.Some embodiments disclosed herein relate to a fluid catalytic crackingapparatus and process for maximizing the conversion of a heavyhydrocarbon feed, such as vacuum gas oil and/or heavy oil residues intovery high yield of light olefins, such as propylene and ethylene,aromatics and gasoline with high octane number.

BACKGROUND

In recent times, production of light olefins via fluid catalyticcracking (FCC) processes has been considered one of the most attractivepropositions. Additionally, there is an ever increasing demand forpetrochemical building blocks such as propylene, ethylene, and aromatics(benzene, toluene, xylenes, etc.). Further, integration of petroleumrefineries with a petrochemicals complex has become a preferred optionfor both economic and environmental reasons.

Global trends also show that there is increased demand for middledistillates (diesel) than that of gasoline product. In order to maximizemiddle distillates from FCC process, it is required to operate FCC atlower reactor temperature and a different catalyst formulation. Thedownside of such change is decreased light olefins yield because of FCCunit operating at much lower reactor temperature. This will also reducefeedstock for Alkylation units.

Several fluidized bed catalytic processes have been developed over thelast two decades, adapting to the changing market demands. For example,U.S. Pat. No. 7,479,218 discloses a fluidized catalytic reactor systemin which a riser-reactor is divided into two sections of different radiiin order to improve the selectivity for light olefins production. Thefirst part of the riser reactor with lesser radii is employed forcracking heavy feed molecules to naphtha range. The enlarged radiiportion, the second part of the riser reactor is used for furthercracking of naphtha range products into light olefins such as propylene,ethylene, etc. Though the reactor system concept is fairly simple, thedegree of selectivity to light olefins is limited for the followingreasons: (1) the naphtha range feed streams contact partially coked ordeactivated catalyst; (2) the temperature in the second part of thereaction section is much lower than the first zone because of theendothermic nature of the reaction in both sections; and (3) lack of thehigh activation energy required for light feed cracking as compared tothat of heavy hydrocarbons.

U.S. Pat. Nos. 6,106,697, 7,128,827, and 7,323,099 employ two stagefluid catalytic cracking (FCC) units to allow a high degree of controlfor selective cracking of heavy hydrocarbons and naphtha range feedstreams. In the 1^(st) stage FCC unit, consisting of a riser reactor,stripper and regenerator for converting gas oil/heavy hydrocarbon feedsinto naphtha boiling range products, in the presence of Y-type largepore zeolite catalyst. A 2^(nd) stage FCC unit with a similar set ofvessels/configuration is used for catalytic cracking of recycled naphthastreams from the 1^(st) stage. Of course, the 2^(nd) stage FCC unitemploys a ZSM-5 type (small pore zeolite) catalyst to improve theselectivity to light olefins. Though this scheme provides a high degreeof control over the feed, catalyst and operating window selection andoptimization in a broad sense, the 2^(nd) stage processing of naphthafeed produces very little coke that is insufficient to maintain the heatbalance. This demands heat from external sources to have adequatetemperature in the regenerator for achieving good combustion and tosupply heat for feed vaporization and endothermic reaction. Usually,torch oil is burned in the 2^(nd) stage FCC regenerator, which leads toexcessive catalyst deactivation due to higher catalyst particletemperatures and hot spots.

U.S. Pat. No. 7,658,837 discloses a process and device to optimize theyields of FCC products by utilizing a part of a conventional stripperbed as a reactive stripper. Such reactive stripping concept of secondreactor compromises the stripping efficiency to some extent and hencemay lead to increased coke load to regenerator. The product yield andselectivity is also likely to be affected due to contact of the feedwith coked or deactivated catalyst. Further, reactive strippertemperatures cannot be changed independently because the riser toptemperature is directly controlled to maintain a desired set ofconditions in the riser.

US2007/0205139 discloses a process to inject hydrocarbon feed through afirst distributor located at the bottom section of the riser formaximizing gasoline yield. When the objective is to maximize lightolefins, the feed is injected at the upper section of the riser througha similar feed distribution system with an intention to decrease theresidence time of hydrocarbon vapors in the riser.

WO2010/067379 aims at increasing propylene and ethylene yields byinjecting C₄ and olefinic naphtha streams in the lift zone of the riserbelow the heavy hydrocarbon feed injection zone. These streams not onlyimprove the light olefins yield but also act as media for catalysttransport in place of steam. This concept helps in reducing the degreeof thermal deactivation of the catalyst. However, this lacks inflexibility of varying operating conditions such as temperature and WHSVin the lift zone, which are critical for cracking of such light feedsteams. This is likely to result in inferior selectivity to the desiredlight olefins.

U.S. Pat. No. 6,869,521 discloses that contacting a feed derived fromFCC product (particularly naphtha) with a catalyst in a second reactoroperating in fast fluidization regime is useful for promoting hydrogentransfer reactions and also for controlling catalytic crackingreactions.

U.S. Pat. No. 7,611,622 discloses an FCC process employing dual risersfor converting a C₃/C₄ containing feedstock to aromatics. The first andsecond hydrocarbon feeds are supplied to the respective 1^(st) and2^(nd) risers in the presence of gallium enriched catalyst and the2^(nd) riser operates at higher reaction temperature than the first.

U.S. Pat. No. 5,944,982 discloses a catalytic process with dual risersfor producing low sulfur and high octane gasoline. The second riser isused to process recycle the heavy naphtha and light cycle oils afterhydro-treatment to maximize the gasoline yield and octane number.

US20060231461 discloses a process that maximizes production of lightcycle oil (LCO) or middle distillate product and light olefins. Thisprocess employs a two reactor system where the first reactor (riser) isused for cracking gas oil feed into predominantly LCO and a secondconcurrent dense bed reactor is used for cracking of naphtha recycledfrom the first reactor. This process is limited by catalyst selectivityand lacks in the desired level of olefins in naphtha due to operation ofthe first reactor at substantially lower reaction temperatures.

U.S. Pat. No. 6,149,875 deals with removal of feed contaminants such asconcarbon and metals with adsorbent. The FCC catalyst is separated fromadsorbent using the differences between transport/terminal velocity ofthe FCC catalyst and adsorbent.

U.S. Pat. No. 7,381,322 disclosed an apparatus and process to separatecatalyst from a metal adsorbent in stripper cum separator, before aregeneration step for eliminating the adverse effects of contaminantmetals deposited on the adsorbent. This patent employs the difference inminimum/bubbling velocity differences and the application is mainly tosegregate FCC catalyst from adsorbent.

SUMMARY

It has been found that it is possible to use a two-reactor scheme tocrack hydrocarbons, including cracking of a C₄, lighter C₅ fraction,naphtha fraction, methanol, etc. for the production of light olefins,where the two-reactor scheme does not have limitations on selectivityand operability, meets heat balance requirements, and also maintains alow piece count. Select embodiments disclosed herein use a conventionalriser reactor in combination with a mixed flow (e.g., including bothcounter-current and co-current catalyst flows) fluidized bed reactordesigned for maximizing light olefins production. The effluents from theriser reactor and mixed flow reactor are processed in a common catalystdisengagement vessel, and the catalysts used in each of the riserreactor and the mixed flow reactor may be regenerated in a commoncatalyst regeneration vessel. This flow scheme is effective formaintaining a high cracking activity, overcomes the heat balanceproblems, and also improves yield and selectivity of light olefins fromvarious hydrocarbon streams, yet simplifies the product quenching andunit hardware, as will be described in more detail below.

In one aspect, embodiments disclosed herein relate to a process for theconversion or catalytic cracking of hydrocarbons. The process mayinclude feeding a hydrocarbon, a first particle and a second particle toa reactor, where the first particle has a smaller average particle sizeand/or is less dense than the second particle, and where the first andsecond particles may be catalytic or non-catalytic. A first portion ofthe second particle may be recovered as a bottoms product from thereactor; and a cracked hydrocarbon effluent, a second portion of thesecond particle, and the first particle may be recovered as an overheadproduct from the reactor. The second portion of the second particle maybe separated from the overhead product to provide a first streamcomprising the first particle and the hydrocarbon effluent and a secondstream comprising the separated second particle, allowing return of theseparated second particle in the second stream to the reactor.

In another aspect, embodiments disclosed herein relate to a system forthe catalytic cracking of hydrocarbons. The system may include a firstreactor for contacting a first and a second cracking catalyst with ahydrocarbon feedstock to convert at least a portion of the hydrocarbonfeedstock to lighter hydrocarbons. An overhead product line provides forrecovering from the first reactor a first stream comprising firstcracking catalyst, a first portion of the second cracking catalyst, andhydrocarbons. A bottoms product line provides for recovering from thefirst reactor a second stream comprising a second portion of the secondcracking catalyst. A separator may be used for separating secondcracking catalyst from the first stream, producing a hydrocarboneffluent comprising hydrocarbons and the first cracking catalyst. A feedline is provided for returning separated second cracking catalyst fromthe separator to the first reactor.

The system for catalytic cracking of hydrocarbons may also include ariser reactor for contacting a mixture of the first cracking catalystand the second cracking catalyst with a second hydrocarbon feedstock toconvert at least a portion of the second hydrocarbon feedstock tolighter hydrocarbons and recover a riser reactor effluent comprising thelighter hydrocarbons and the mixture of the first cracking catalyst andthe second cracking catalyst. A second separator may be provided forseparating the second cracking catalyst from the hydrocarbon effluentand for separating the mixture of first and second cracking catalystsfrom the riser reactor effluent. A catalyst regenerator for regeneratingfirst and second cracking catalyst recovered in the second separator andthe second portion of the first cracking catalyst recovered in thebottoms product line may also be used.

In another aspect, embodiments disclosed herein relate to a process forthe conversion of hydrocarbons. The process may include: feeding a firstcatalyst to a reactor; feeding a second catalyst to the reactor, whereinthe first catalyst has a smaller average particle size and/or is lessdense than the first catalyst, and feeding a hydrocarbon feedstock tothe reactor. An overhead effluent may be recovered from the reactor, theeffluent including cracked hydrocarbon, the first catalyst, and thesecond catalyst. The second catalyst may be separated from the overheadproduct to provide a first stream comprising the first catalyst and thehydrocarbon effluent and a second stream comprising the separated secondcatalyst, allowing return of the separated second catalyst in the secondstream to the reactor.

In another aspect, embodiments herein are directed toward a separatorfor separating catalysts or other particles based on size and/or densitydifference. The separator may have a minimum of one inlet and may alsohave a minimum of two outlets for separating particles from carriergases. The carrier gas enters the separator with the particles whereuponinertial, centrifugal and/or gravitational forces may be exerted on theparticles such that a portion of the particles and carrier gas arecollected in the first outlet and a portion of the particles along withthe carrier gas are collected in the second outlet. The combination offorces in the separator may have the effect of enriching an outletstream in particle size and/or density versus the inlet concentration.The separator may have additional carrier gas distribution orfluidization inside of the vessel/chamber to exert additional forces onthe particles which may facilitate enhanced classification.

In another aspect, embodiments herein are directed toward an inertialseparator for separating catalysts or other particles based on sizeand/or density. The inertial separator may include an inlet forreceiving a mixture comprising a carrier gas, a first particle type, anda second particle type. Each particle type may have an average particlesize and a particle size distribution, which may be different oroverlapping, and an average density. The second particle type may havean average particle size and/or average density greater than the firstparticle type. The inertial separator may include a U-shaped conduitincluding a first vertical leg, a base of the U-shape, and a secondvertical leg. The U-shaped conduit may fluidly connect the inlet via thefirst vertical leg to a first outlet and a second outlet, the firstoutlet being connected proximate the base of the U-shaped conduit andthe second outlet being connected to the second vertical leg. TheU-shaped inertial separator may be configured to: separate at least aportion of the second particle type from the carrier gas and the firstparticle type, recover the second particle type via the first outlet,and recover the carrier gas and the first particle type via the secondoutlet. The separator may also include a distributor disposed within orproximate the second outlet for introducing a fluidizing gas,facilitating additional separation of the first particle type from thesecond particle type. The separator, in some embodiments, may beconfigured such that a cross-sectional area of the U-shaped conduit or aportion thereof is adjustable. For example, in some embodiments theseparator may include a movable baffle disposed within one or moresections of the U-shaped conduit.

In another aspect, embodiments herein are directed toward an inertialseparator for separating catalysts or other particles based on sizeand/or density as above. The inertial separator may include an inlethorizontal conduit which traverses a chamber before being deflected by abaffle. The chamber is connected to a first vertical outlet and a firsthorizontal outlet. The baffle may be located in the middle, proximatethe inlet, or proximate the outlet of the chamber. The baffle may be atan angle or moveable such that to deflect more or less catalystparticles. The baffle chamber separator may be configured to: separateat least a portion of the second particle type from the carrier gas andthe first particle type, recover the second particle type via the firstvertical outlet and recover the carrier gas and the first particle typevia the first horizontal outlet. The separator may also include adistributor disposed within or proximate the first vertical outlet forintroducing a fluidizing gas, facilitating additional separation of thefirst particle type from the second particle type.

In another aspect, embodiments herein are directed toward an inertialseparator for separating catalysts or other particles based on sizeand/or density as above. The inertial separator may include a verticalinlet connected to a chamber where one or more vertical sides of thechamber are equipped with narrow slot outlets, which may be described aslouvers. The number of louvers may vary depending on the application andthe angle of the louver may be adjustable in order to control the amountof vapor leaving the louver outlets. The chamber is also connected to afirst vertical outlet at the bottom of the chamber. The louver separatormay be configured to: separate at least a portion of the second particletype from the carrier gas and the first particle type, recover thesecond particle type via the first vertical outlet and recover thecarrier gas and the first particle type via the louver outlets. Theseparator may also include a distributor disposed within or proximatethe first vertical outlet for introducing for introducing a fluidizinggas, facilitating additional separation of the first particle type fromthe second particle type.

The above described separators may also be used in association withreactors, regenerators, and catalyst feed systems to enhance systemperformance and flexibility.

In one aspect, embodiments disclosed herein relate to a process for theconversion of hydrocarbons. The process may include regenerating acatalyst mixture comprising a first catalyst and a second particle in aregenerator, wherein the first catalyst has a smaller average particlesize and/or is less dense than the second particle, and wherein thesecond particle may be catalytic or non-catalytic. The catalyst mixtureand hydrocarbons may be fed to a riser reactor to convert at least aportion of the hydrocarbons and recover a first effluent comprising thecatalyst mixture and converted hydrocarbons. The catalyst mixture mayalso be fed to a second reactor. Feeding a hydrocarbon feedstock to thesecond reactor and fluidizing the catalyst mixture may contact thehydrocarbon feedstock with the catalyst mixture to convert thehydrocarbons and provide for recovering an overhead product from thesecond reactor comprising the second particle, the first catalyst, and areacted hydrocarbon product. The second particle may then be separatedfrom the overhead product to provide a first stream comprising the firstcatalyst and the reacted hydrocarbon product and a second streamcomprising the separated second particle, returning the separated secondparticle in the second stream to the reactor.

In another aspect, embodiments disclosed herein relate to a process forthe conversion of hydrocarbons. The process may include withdrawing amixture comprising a first catalyst and a second catalyst from acatalyst regenerator and feeding the mixture and hydrocarbons to a riserreactor to convert at least a portion of the hydrocarbons and recover afirst effluent comprising the catalyst mixture and convertedhydrocarbons, wherein the first catalyst has a smaller average particlesize and/or is less dense than the second catalyst. The process may alsoinclude withdrawing the mixture comprising a first catalyst and a secondcatalyst from the catalyst regenerator and feeding the mixture to acatalyst separation system, fluidizing the mixture comprising the firstcatalyst and the second catalyst with a fluidization medium, andseparating the first catalyst from the second catalyst in the catalystseparation system to recover a first stream comprising the firstcatalyst and the fluidization medium and a second stream comprising thesecond catalyst. A hydrocarbon feedstock and either the first stream orthe second stream may then be fed to a reactor to react at least aportion of the hydrocarbon to produce a converted hydrocarbon.

In another aspect, embodiments disclosed herein relate to a process forthe conversion of hydrocarbons. The process may include feeding ahydrocarbon feedstock and a catalyst mixture comprising a first catalystand a second catalyst to a riser reactor, wherein the first catalyst hasa smaller average particle size and/or is less dense than the secondcatalyst. An effluent from the riser reactor may then be separated torecover a first stream comprising the first catalyst and convertedhydrocarbon feedstock and a second stream comprising the secondcatalyst, and the second stream may be fed to the riser reactor.

In another aspect, embodiments disclosed herein relate to a process forthe conversion of hydrocarbons. The process may include withdrawing amixture comprising a first catalyst and a second catalyst from acatalyst regenerator and feeding the mixture to a catalystfeed/separation system, wherein the first catalyst has a smaller averageparticle size and/or is less dense than the second catalyst. The firstcatalyst may be separated from the second catalyst in the catalystfeed/separation system to produce a first stream comprising the firstcatalyst and a second stream comprising the second catalyst. Ahydrocarbon feedstock and either the first stream or the second streammay then be fed to a riser reactor to react at least a portion of thehydrocarbon to produce a converted hydrocarbon.

In another aspect, embodiments disclosed herein relate to a system forthe conversion of hydrocarbons. The system may include a catalystregenerator, and a first catalyst feed line for withdrawing a mixturecomprising a first catalyst and a second catalyst from the catalystregenerator and feeding the mixture to a riser reactor, wherein thefirst catalyst has a smaller average particle size and/or is less densethan the second catalyst. The system may also include a second catalystfeed line for withdrawing the mixture comprising a first catalyst and asecond catalyst from the catalyst regenerator and feeding the mixture toa catalyst separation system, and a fluidization medium feed line forfluidizing the mixture withdrawn via the second catalyst feed line witha fluidization medium and separating the first catalyst from the secondcatalyst in the catalyst separation system to recover a first streamcomprising the first catalyst and the fluidization medium and a secondstream comprising the second catalyst. A reactor may be provided forcontacting a hydrocarbon feedstock and either the first stream or thesecond stream to react at least a portion of the hydrocarbon to producea converted hydrocarbon.

In another aspect, embodiments disclosed herein relate to a system forthe conversion of hydrocarbons. The system may include a riser reactorfor contacting a hydrocarbon feedstock with a catalyst mixturecomprising a first catalyst and a second catalyst, wherein the firstcatalyst has a smaller average particle size and/or is less dense thanthe second catalyst. A catalyst separation system is provided forseparating a riser reactor effluent to recover a first stream comprisingthe first catalyst and converted hydrocarbon feedstock and a secondstream comprising the second catalyst. A flow line feeds the secondstream to the riser reactor.

In another aspect, embodiments disclosed herein relate to a system forthe conversion of hydrocarbons. The system may include a catalystwithdrawal line for withdrawing a mixture comprising a first catalystand a second catalyst from a catalyst regenerator and feeding themixture to a catalyst feed/separation system, wherein the first catalysthas a smaller average particle size and/or is less dense than the secondcatalyst. The catalyst feed/separation system separates the firstcatalyst from the second catalyst in the catalyst feed/separation systemto produce a first stream comprising the first catalyst and a secondstream comprising the second catalyst. A riser reactor contacts ahydrocarbon feedstock and either the first stream or the second streamto react at least a portion of the hydrocarbon to produce a convertedhydrocarbon.

The apparatus and processes disclosed herein use significantly differenttechnique than disclosed in the above patents (such as U.S. Pat. Nos.6,149,875 and 7,381,322) to separate particulate mixtures. The purposeof the present disclosure is also different; the prior art disclosuresfocus on removing the contaminants from the catalyst by introducing anadsorbent. However, the present invention aims at improving theconversion, selectivity and heat balance by concentrating a selectedcatalyst in a reactor, such as concentrating the ZSM-5/11 in the secondreactor.

In summary, most of the state of the art included dual riser/reactorconfigurations or two stage fluid catalytic cracking processschemes/apparatus. The second/parallel reactor used for processing lightfeed (naphtha or/and C4 streams) are either concurrent pneumatic flowriser type or dense bed reactors. It is well known in the art that ZSM-5is preferable catalyst/additive to convert naphtha/C4 streams intopropylene and ethylene. However, in processes employing two reactors,the second reactor also receives Y-zeolite catalyst with small fractionsof ZSM-5 additive. In other process schemes, FCC typereactor-regenerator concepts are employed for maximizing light olefinsfrom naphtha/C4 streams. Such schemes pose heat balance problems due toinsufficient coke production. The processes and systems disclosed hereinconsiders separating catalysts, such as ZSM-5 or ZSM-11 additive fromY-zeolite & ZSM-5/ZSM-11, in a mixture, so as to have optimalconcentration of ZSM-5 or 11 in the second reactor processing lightfeed. In addition, integration of said additional/second reactor with aconventional FCC unit essentially helps overcoming these drawbacks(product selectivity and heat balance in particular) of the prior partand substantially increases the overall conversion and light olefinsyield and increases the capability to process heavier feedstocks.

Other aspects and advantages will be apparent from the followingdescription and the appended claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a simplified process flow diagram of a system for crackinghydrocarbons and producing light olefins according to one or moreembodiments disclosed herein.

FIGS. 2-5 are simplified process flow diagrams of separators useful insystems according to one or more embodiments disclosed herein.

FIG. 6 is a simplified process flow diagram of a system for crackinghydrocarbons and producing light olefins according to one or moreembodiments disclosed herein.

FIG. 7 is a simplified process flow diagram of a system for crackinghydrocarbons and producing light olefins according to one or moreembodiments disclosed herein.

FIG. 8A is a simplified process flow diagram of a system for crackinghydrocarbons and producing light olefins according to one or moreembodiments disclosed herein.

FIG. 8B is a simplified process flow diagram of a system for crackinghydrocarbons and producing light olefins according to one or moreembodiments disclosed herein.

FIG. 9A is a simplified process flow diagram of a system for crackinghydrocarbons and producing light olefins according to one or moreembodiments disclosed herein.

FIG. 9B is a simplified process flow diagram of a system for crackinghydrocarbons and producing light olefins according to one or moreembodiments disclosed herein.

FIG. 10 is a simplified process flow diagram of a system for crackinghydrocarbons and producing light olefins according to one or moreembodiments disclosed herein.

FIG. 11 is a simplified process flow diagram of a system for crackinghydrocarbons and producing light olefins according to one or moreembodiments disclosed herein.

DETAILED DESCRIPTION

As used herein, the terms “catalyst” and “particle” and like terms maybe used interchangeably. Summarized above, and as further describedbelow, embodiments herein separate mixed particulate materials based onsize and/or density to achieve an advantageous effect in a reactorsystem. The particles or particulate materials used to facilitatecatalytic or thermal reaction may include catalysts, absorbents, and/orheat transfer materials having no catalytic activity, for example.

In one aspect, embodiments herein relate to a fluid catalytic crackingapparatus and process for maximizing the conversion of a heavyhydrocarbon feed, such as vacuum gas oil and/or heavy oil residues intovery high yield of light olefins, such as propylene and ethylene,aromatics and gasoline with high octane number or middle distillates,while concurrently minimizing the yield of heavier bottom product. Toaccomplish this goal, a secondary reactor, which may be a mixed flowreactor (including both co-current and counter-current flow of particleswith respect to vapor flow) or a catalyst-concentrating reactor, can beintegrated with a conventional fluid catalytic cracking reactor, such asa riser reactor. A heavy hydrocarbon feed is catalytically cracked tonaphtha, middle distillates and light olefins in the riser reactor,which is a pneumatic flow co-current type reactor. To enhance the yieldsand selectivity to light olefins (ethylene and propylene), crackedhydrocarbon products from the riser reactor, such as C₄ and naphtharange hydrocarbons (olefins and paraffins), may be recycled andprocessed in the secondary reactor (the mixed flow reactor or thecatalyst-concentrating reactor). Alternatively, or additionally,external feed streams, such as C₄, naphtha, or other hydrocarbonfractions from other processes such as a steam cracker, metathesisreactor, or delayed coking unit, and naphtha range streams, such asstraight run naphtha or from delayed coking, visbreaking or natural gascondensates, among other hydrocarbon feedstocks, may be processed in thesecondary reactor to produce light olefins, such as ethylene andpropylene. The integration of the secondary reactor with a conventionalFCC riser reactor according to embodiments disclosed herein may overcomethe drawbacks of prior processes, may substantially increase the overallconversion and light olefins yield, and/or may increases the capabilityto process heavier feedstocks.

Integration of the secondary reactor with a conventional FCC riserreactor according to embodiments disclosed herein may be facilitated by(a) using a common catalyst regeneration vessel, (b) using two types ofcatalyst, one being selective for cracking heavier hydrocarbons and theother being selective for the cracking of C₄ and naphtha rangehydrocarbons for the production of light olefins, and (c) using a mixedflow reactor or a catalyst-concentrating reactor in a flow regime thatwill partially separate the two types of catalysts, favoring the contactof the C₄s or naphtha feed with the catalyst selective for cracking thesame and producing light olefins.

To enhance the operation window of the secondary reactor, and to providegreater process flexibility, the secondary reactor may be operated in aflow regime to entrain the catalyst selective for cracking heavierhydrocarbons, and to entrain a portion of the catalyst selective for thecracking of C₄ and naphtha range hydrocarbons. The cracked hydrocarbonproducts and the entrained catalysts are then fed to a separator toseparate the catalyst selective for the cracking of C₄ and naphtha rangehydrocarbons from the cracked hydrocarbon products and the catalystselective for cracking heavier hydrocarbons. This solids separationvessel is an external vessel to the reactor and is operated athydrodynamic properties that enhance the separation of the two types ofcatalyst based on their physical properties, such as particle sizeand/or density. The separated catalyst, selective for the cracking of C₄and naphtha range hydrocarbons, may then be returned to the reactor forcontinued reaction and providing an enhanced concentration of thecatalyst selective for the cracking of C₄ and naphtha range hydrocarbonswithin the reactor, improving selectivity of the overall process whilealso improving the overall process flexibility due to the enhancedoperating window.

As noted above, the cracking system may utilize two types of catalysts,each favoring a different type of hydrocarbon feed. The first crackingcatalyst may be a Y-type zeolite catalyst, an FCC catalyst, or othersimilar catalysts useful for cracking heavier hydrocarbon feedstocks.The second cracking catalyst may be a ZSM-5 or ZSM-11 type catalyst orsimilar catalyst useful for cracking C₄s or naphtha range hydrocarbonsand selective for producing light olefins. To facilitate the two-reactorscheme disclosed herein, the first cracking catalyst may have a firstaverage particle size and density, and may be smaller and/or lighterthan those for the second cracking catalyst, such that the catalysts maybe separated based on density and/or size (e.g., based on terminalvelocity or other characteristics of the catalyst particles).

In the catalyst regeneration vessel, spent catalyst recovered from boththe riser reactor and the secondary reactor is regenerated. Followingregeneration, a first portion of the mixed catalyst may be fed from theregeneration vessel to a riser reactor (co-current flow reactor). Asecond portion of the mixed catalyst may be fed from the regenerationvessel to the secondary reactor.

In the co-current flow reactor, a first hydrocarbon feed is contactedwith a first portion of the regenerated catalyst to crack at least aportion of the hydrocarbons to form lighter hydrocarbons. An effluentmay then be recovered from the co-current flow reactor, the effluentcomprising a first cracked hydrocarbon product and a spent mixedcatalyst fraction.

In some embodiments, the secondary reactor is operated in a fluidizationregime sufficient to entrain the first cracking catalyst, and the secondcracking catalyst with the hydrocarbon products recovered as an effluentfrom the secondary reactor overhead outlet. The effluent is then fed toa separator to separate the cracked hydrocarbon products and the firstcracking catalyst from the second cracking catalyst.

The vapor/first cracking catalyst stream recovered from the separatormay then be forwarded for separation. The second cracking catalystrecovered from the separator may be recycled back to the secondaryreactor for continued reaction, as noted above.

The first effluent (cracked hydrocarbons and spent mixed catalyst fromthe riser reactor) and the second effluent (cracked hydrocarbons andseparated first cracking catalyst from the secondary reactor) may bothbe fed to a disengagement vessel to separate the spent mixed catalystfraction and the separated first cracking catalyst from the first andsecond cracked hydrocarbon products. The cracked hydrocarbon products,including light olefins, C₄ hydrocarbons, naphtha range hydrocarbons,and heavier hydrocarbons may then be separated to recover the desiredproducts or product fractions.

Thus, processes disclosed herein integrate a secondary mixed-flow orcatalyst-concentrating reactor, external solids separator, and a riserreactor, with common product separations and catalyst regeneration,where the catalysts used in the secondary reactor is highly selectivefor cracking C₄ and naphtha range hydrocarbons to produce light olefins.The common catalyst regeneration provides for heat balance, and thecommon product separation (disengagement vessel, etc.) provides forsimplicity of operations and reduced piece count, among otheradvantages.

Referring now to FIG. 1, a simplified process flow diagram of systemsfor cracking hydrocarbons and producing light olefins according toembodiments disclosed herein is illustrated. The system includes atwo-reactor configuration for maximizing yield of propylene and ethylenefrom petroleum residue feedstocks or other hydrocarbon streams. Thefirst reactor 3 may be a riser reactor for cracking heavier hydrocarbonfeeds, for example. The second reactor 32 is a fluidized bed reactor,which may be equipped with baffles or internals. The C₄ olefins and/orlight naphtha products from the first reactor 3 or similar feed streamsfrom external sources may be processed in the second reactor 32 toenhance the yield of light olefins, including propylene and ethylene,and aromatics/high octane gasoline.

A heavy petroleum residue feed is injected through one or more feedinjectors 2 located near the bottom of first reactor 3. The heavypetroleum feed contacts hot regenerated catalyst introduced through aJ-bend 1. The catalyst fed to the first reactor 3 is a catalyst mixture,including a first catalyst selective for cracking heavier hydrocarbons,such as a Y-type zeolite based catalyst, and a second catalyst selectivefor the cracking of C₄ and naphtha range hydrocarbons for the productionof light olefins, such as a ZSM-5 or ZSM-11, which may also be used incombination with other catalysts. The first and second catalysts may bedifferent in one or both particle size and density. A first catalyst,such as the Y-type based zeolite, may have a particle size in the rangeof 20-200 microns and an apparent bulk density in the range of 0.60-1.0g/ml. A second catalyst, such as ZSM-5 or ZSM-11, may have a particlesize in the range of 20-350 microns and an apparent bulk density in therange of 0.7-1.2 g/ml.

The heat required for vaporization of the feed and/or raising thetemperature of the feed to the desired reactor temperature, such as inthe range from 500° C. to about 700° C., and for the endothermic heat(heat of reaction) may be provided by the hot regenerated catalystcoming from the regenerator 17. The pressure in first reactor 3 istypically in the range from about 1 barg to about 5 barg.

After the major part of the cracking reaction is completed, the mixtureof products, unconverted feed vapors, and spent catalyst flow into a twostage cyclone system housed in cyclone containment vessel 8. Thetwo-stage cyclone system includes a primary cyclone 4, for separatingspent catalyst from vapors. The spent catalyst is discharged intostripper 9 through primary cyclone dip leg 5. Fine catalyst particlesentrained with the separated vapors from primary cyclone 4 and productvapors from second reactor 32, introduced via flow line 36 a and asingle stage cyclone 36 c, are separated in second stage cyclone 6. Thecatalyst mixture collected is discharged into stripper 9 via dip leg 7.The vapors from second stage cyclone 6 are vented through a secondarycyclone outlet 12 b, which may be connected to plenum 11, and are thenrouted to a main fractionator/gas plant (not shown) for recovery ofproducts, including the desired olefins. If necessary, the productvapors are further cooled by introducing light cycle oil (LCO) or steamvia distributor line 12 a as a quench media.

The spent catalyst recovered via dip legs 5, 7 undergoes stripping instripper bed 9 to remove interstitial vapors (the hydrocarbon vaporstrapped between catalyst particles) by countercurrent contacting ofsteam, introduced to the bottom of stripper 9 through a steamdistributor 10. The spent catalyst is then transferred to regenerator 17via the spent catalyst standpipe 13 a and lift line 15. Spent catalystslide valve 13 b, located on spent catalyst standpipe 13 a is used forcontrolling catalyst flow from stripper 9 to regenerator 17. A smallportion of combustion air or nitrogen may be introduced through adistributor 14 to help smooth transfer of spent catalyst.

Coked or spent catalyst is discharged through spent catalyst distributor16 in the center of the dense regenerator bed 24. Combustion air isintroduced by an air distributor 18 located at the bottom of regeneratorbed 24. Coke deposited on the catalyst is then burned off in regenerator17 via reaction with the combustion air. Regenerator 17, for example,may operate at a temperature in the range from about 640° C. to about750° C. and a pressure in the range from about 1 barg to about 5 barg.The catalyst fines entrained along with flue gas are collected in firststage cyclone 19 and second stage cyclone 21 and are discharged into theregenerator catalyst bed through respective dip legs 20, 22. The fluegas recovered from the outlet of second stage cyclone 21 is directed toflue gas line 50 via regenerator plenum 23 for downstream waste heatrecovery and/or power recovery.

A first part of the regenerated catalyst mixture is withdrawn viaregenerated catalyst standpipe 27, which is in flow communication with Jbend 1. The catalyst flow from regenerator 17 to reactor 3 may beregulated by a slide valve 28 located on regenerated catalyst standpipe27. The opening of slide valve 28 is adjusted to control the catalystflow to maintain a desired top temperature in reactor 3.

In addition to lift steam, a provision is also made to inject feedstreams such as C₄ olefins and naphtha or similar external streams as alift media to J bend 1 through a gas distributor 1 a located at theY-section for enabling smooth transfer of regenerated catalyst from Jbend 1 to reactor 3. J bend 1 may also act as a dense bed reactor forcracking C₄ olefins and naphtha streams into light olefins at conditionsfavorable for such reactions, such as a WHSV of 0.5 to 50 h⁻¹, atemperature of 640° C. to 750° C., and residence times from 3 to 10seconds.

A second part of the regenerated catalyst mixture is withdrawn into asecond reactor 32 through a standpipe 30. A slide valve 31 may be usedto control the catalyst flow from regenerator 17 to second reactor 32based on a vapor outlet temperature set point. C₄ olefins and naphthastreams are injected into the bottom section of the catalyst bed throughone or more feed distributors 34 (34 a, 34 b), either in liquid or vaporphase. Second reactor 32 operates in a mixed flow fashion, where aportion of the regenerated catalyst flows downward (from the top to thebottom of the reactor bed) and a portion of the regenerated catalystmixture and the feed hydrocarbon stream flows upward (from the bottom tothe top of the reactor bed).

Second reactor 32 may be equipped with baffles or structured internals(not shown) that help intimate contact and mixing of catalyst and feedmolecules. These internals may also help in minimizing channeling,bubble growth, and/or coalescence. Second reactor 32 may also beenlarged at different sections along the length to maintain a constantor desired superficial gas velocity within the sections.

After the reaction is completed, the catalyst is stripped at thebottommost portion of second reactor 32 to separate entrainedhydrocarbon feed/products using steam as a stripping media introducedthrough distributor 35. The spent catalyst recovered at the bottom ofreactor 32 is then transferred to regenerator 17 via standpipe 37 andlift line 40 through a spent catalyst distributor 41. Combustion air ornitrogen may be introduced through distributor 39 to enable smoothtransfer of catalyst to regenerator 17. Slide valve 38 may be used tocontrol the catalyst flow from second reactor 32 to regenerator 17.Spent catalyst from both reactors 3, 32 is then regenerated in thecommon regenerator 17, operating in a complete combustion mode.

As noted above, second reactor 32 utilizes two different catalysts thatmay differ in one or both of particle size and density, such as alighter and smaller Y-type zeolite or FCC catalyst and a larger and/ordenser ZSM-5/ZSM-11 shape-selective pentacil small pore zeolite. Thesuperficial gas velocity in second reactor 32 is maintained such thatessentially all or a large portion of the lighter, smaller catalyst(e.g., Y-type zeolite/FCC catalyst) and a portion of the heavier, largercatalyst (e.g., ZSM-5/ZSM-11) is carried out of the reactor with thecracked hydrocarbons and steam recovered via flow line 45. A portion ofthe larger and/or denser catalyst may be retained within the reactor 32,forming a dense bed toward the lower portion of the reactor, as notedabove.

The effluent from reactor 32 recovered via flow line 45 may thus includecracked hydrocarbon products, unreacted hydrocarbon feedstock, steam(stripping media), and a catalyst mixture, including essentially all ofthe lighter and/or smaller catalyst and a portion of the larger and/ormore dense catalyst introduced to the reactor. The effluent may then betransported via flow line 45 to a solids separator 47. Separator 47 maybe a separator configured to separate the two types of catalyst based ontheir physical properties, namely particle size and/or density. Forexample, separator 47 may use differences in inertial forces orcentrifugal forces to separate FCC catalyst from the ZSM-5. The solidsseparation vessel 47 is an external vessel to the second reactor 32 andis operated at hydrodynamic properties that enhance the separation ofthe two types of catalyst based on their physical properties.

After separation in separator 47, the smaller and/or lighter catalyst(Y-type zeolite/FCC catalyst) is then transported from separator 47 tothe common disengager or containment vessel 8, housing the riser reactorcyclones and/or reaction termination system, via outlet line 36 a. Thelarger and/or denser catalyst (ZSM-5/ZSM-11) may be returned via flowline 49 to the mixed flow reactor 32 for continued reaction withhydrocarbon feeds introduced through distributors 34.

Entrainment of essentially all of the lighter/smaller catalyst and aportion of the larger and/or more dense catalyst, subsequentseparations, and recycle of the larger and/or denser catalyst to reactor32 may allow for a significant accumulation of the larger and/or densercatalyst in reactor 32. As this catalyst is more selective for thecracking of C₄ and naphtha range hydrocarbons, the accumulation of thelarger and/or denser catalyst may provide a selectivity and yieldadvantage. Further, operation of the reactor in a fluidization flowregime to entrain both types of catalyst may provide for improvedoperability of the reactor or flexibility in operations, as discussedabove.

A hydrocarbon feed such as heavy vacuum gas oil or heavy residue feed,light cycle oil (LCO), or steam may be injected as a quench media in theoutlet line 36 a through a distributor 36 b. The flow rate of suchquench media may be controlled by setting the temperature of the streamentering the containment vessel 8. All the vapors from second reactor32, including those fed through distributor 36 b, are discharged intothe dilute phase of containment vessel 8 through a single stage cyclone36 c. Employing a hydrocarbon feed as a quench media is preferred as itserves dual purpose of cooling the products from second reactor 32 andalso enhances the production of middle distillates.

The first stage reactor 3, such as a riser reactor, may operates in thefast fluidization regime (e.g., at a gas superficial velocity in therange from about 3 to about 10 m/s at the bottom section) and pneumatictransport regime (e.g., at a gas superficial velocity in the range fromabout 10 to about 20 m/s) in the top section.

WHSV in second reactor 32 is typically in the range from about 0.5 h⁻¹to about 50 h⁻¹; vapor and catalyst residence times may vary from about2 to about 20 seconds. When different feeds are introduced, preferablythe C₄ feed is injected at an elevation below naphtha feed injection.However, interchanging of feed injection locations is possible.

As necessary, make-up catalyst may be introduced via one or more flowlines 42, 43. For example, fresh or make-up FCC or Y-type zeolitecatalyst or a mixture of these two may be introduced to regenerator 17via flow line 42 and fresh or make-up ZSM-5/ZSM-11 catalyst may beintroduced to second reactor 32 via flow line 43. Overall systemcatalyst inventory may be maintained by withdrawing mixed catalyst fromregenerator 24, for example. Catalyst inventory and accumulation of thepreferred catalyst within reactor 32 may be controlled, as will bedescribed below, via control of the reactor and separator 47 operations.

In some embodiments, a first part of the regenerated catalyst iswithdrawn from regenerator 17 into a Regenerated Catalyst (RCSP) hopper26 via withdrawal line 25, which is in flow communication withregenerator 17 and regenerated catalyst standpipe 27. The catalyst bedin the RCSP hopper 26 floats with regenerator 17 bed level. Theregenerated catalyst is then transferred from RCSP hopper 26 to reactor3 via regenerated catalyst standpipe 27, which is in flow communicationwith J bend 1. The catalyst flow from regenerator 17 to reactor 3 may beregulated by a RCSP slide valve 28 located on regenerated catalyststandpipe 27. A pressure equalization line 29 may also be provided.

A separator bypass line 60 may also be used to facilitate the transferof particles from the top of reactor 32 to the vessel 8, such asillustrated in FIG. 1. As described with respect to FIG. 1 above, secondreactor 32 utilizes two different catalysts that may differ in one orboth of particle size and density, such as a lighter and/or smallerY-type zeolite or FCC catalyst and a larger and/or denser ZSM-5/ZSM-11shape-selective pentacil small pore zeolite. The superficial gasvelocity in second reactor 32 may be maintained such that essentiallyall of the lighter, smaller catalyst (e.g., Y-type zeolite/FCC catalyst)and a portion of larger and/or more dense catalyst (e.g., ZSM-5/ZSM-11)is carried out of the reactor with the cracked hydrocarbons and steamrecovered via flow line 45.

The effluent from reactor 32 recovered via flow line 45 may thus includecracked hydrocarbon products, unreacted hydrocarbon feedstock, steam(stripping media), and a catalyst mixture, including essentially all ofthe lighter, smaller catalyst and a portion of the larger and/or moredense catalyst introduced to the reactor. The effluent may then betransported via flow line 45 to a solids separator 47. Separator 47 maybe a separator configured to separate the two types of catalyst based ontheir physical properties, namely particle size and/or density. Theseparator 47 is operated at hydrodynamic properties that enhance theseparation of the two types of catalyst based on their physicalproperties.

After separation in separator 47, the smaller/lighter catalyst (Y-typezeolite/FCC catalyst) is then transported from separator 47 to thecommon disengager or containment vessel 8, housing the riser reactorcyclones and/or reaction termination system, via outlet line 36 a. Thelarger and/or denser catalyst (ZSM-5/ZSM-11) may be returned to themixed flow reactor 32 for continued reaction with hydrocarbon feedsintroduced through distributors 34.

Continuously or intermittently, a portion of the effluent containingboth types of catalysts being transported via flow line 45 may bediverted to bypass separator 47. The diverted portion of the effluentmay flow around separator 47 via flow line 60, which may include adiverter or flow control valve 62. The effluent may then continue viaflow line 64 back to disengager 8 for separation of the hydrocarbonproducts from the catalysts. Flow line 64 may be combined with theeffluent and smaller catalyst recovered from separator 47 via flow line36 a, and may be introduced either upstream or downstream of quench 36b. Alternatively, the diverted effluent in line 60 may be fed directlyto disengager/containment vessel 8.

While illustrated in FIG. 1 with a diverter valve 62, embodiments hereincontemplate use of y-shaped flow conduit or similar apparatus tocontinuously send a portion of the effluent, containing both catalystparticle types, to disengager 8, while continuously sending a portion ofthe effluent to separator 47, thus allowing for the desired accumulationof the larger and/or denser catalyst particles within reactor 32. Asdepicted in FIG. 1, the catalyst from second reactor can also betransferred via line 37, slide valve 38 and transfer line 40 to theregenerator 17. The blower air is used as carrier gas 39 to transfer thecatalyst to regenerator 17. Such catalyst transfer facility will notonly help in controlling the catalyst bed level in reactor 32 but alsohelp in more frequent catalyst regeneration.

The use of increased flow of carrier fluid and/or the use of a flowdiverter, as described above, may beneficially provide for theaccumulation of the catalyst selective for cracking naphtha rangehydrocarbons in the second reactor, reactor 32. In some embodiments, ithas been found that reactor 32 may be operated in a manner to provideregenerated catalyst and maintain sufficient activity within thecatalyst bed of reactor 32 such that the catalyst transfer line (flowlines 37, 40) and the associated equipment may be omitted from the flowscheme (as shown in FIG. 6) without detriment to the selectivity andthroughput of the reactor and with the added benefits of reducedmechanical complexity and reduced capital and operating costs.

Referring now to FIG. 6, a simplified process flow diagram of systemsfor cracking hydrocarbons and producing light olefins according toembodiments disclosed herein is illustrated, where like numeralsrepresent like parts. Similar to the process scheme illustrated in FIG.1, described above, the system as illustrated in FIG. 6 will have a tworeactor scheme and introduce two kinds of particles (such as a lighterand/or smaller Y-type or FCC catalyst and a larger and/or denser ZSM-5or ZSM-11 catalyst) in the secondary reactor 32. The larger and/ordenser catalyst additives (e.g., ZSM-5 or ZSM-11) may be added directlyto the secondary reactor vessel 32 via flow line 43. The regeneratedcatalyst mixture transfers from regenerator 17 through pipe 30 to thereactor vessel 32.

The catalyst bed in the secondary reactor vessel 32 is expected tooperate in turbulent bed, bubbling bed or fast fluidization regimes. Alight naphtha feed 34 a, such as the light naphtha product from aprimary reactor or riser reactor 3, as illustrated, may be fed into thesecondary reactor 32 and converted to light olefins in the presence ofthe mixed catalyst. The lifting gas along with product gas in the vessel32 will lift the solids, including both catalysts, through the pipe 45to the solids separation vessel 47, then back to the regenerator 17. Dueto the differences in size and/or density of the two catalyst particles,most of the ZSM-5 or ZSM-11 catalyst particles will be separated fromthe Y-type or FCC catalyst in the solids separation vessel 47 andtransferred via return line 49 back to the reactor 32. Most of Y-type orFCC catalyst particles will be transferred back to the stripper 8 forgas solid separation.

As compared to other embodiments discussed above, a primary differenceis the absence of a catalyst return line and related control valves andequipment from the bottom of the secondary reactor vessel 32 back to theregenerator vessel 17. As discussed briefly above, such a processconfiguration may still provide for efficient catalyst regeneration, aswell as accumulation and concentration of the desired larger and/ordenser ZSM-5 or ZSM-11 catalyst within reactor 32. It is expected that ahigher concentration of the larger and/or denser catalyst may result ina better performance in the secondary reactor vessel 32, even when thereturn line 37 is removed. This design, with the removal of return line37, also mitigates the mechanical complexity and reduces the capital andoperational costs.

The embodiment without a return line 37 (FIG. 6) also includes steam asa lifting gas. As there is no catalyst outlet at the bottom of thereactor 32, the catalyst will fill up the reactor 32 and in someembodiments no catalyst bed level is observed. The lifting gas alongwith product gas in the vessel 32 will lift the solids, including bothcatalysts, through the pipe 45 to the solids separation vessel 47. Dueto the differences in size and/or density of the two catalyst particles,most of the ZSM-5 or ZSM-11 catalyst particles will be separated fromthe Y-type or FCC catalyst in the solids separation vessel 47 andtransferred via return line 49 back to the reactor 32. Most of Y-type orFCC catalyst particles will be transferred back to the stripper 8 forgas solid separation. As compared to FIG. 1, this design without returnline 37 may lead to a much higher concentration of the larger and/ordenser catalyst, which will result in a better reaction performance inthe reactor 32. Although not illustrated, vessel 32 may include a bottomflange or outlet allowing the vessel to be de-inventoried of catalyst.Such an outlet may also be used to periodically remove larger and/orheavier catalyst particles that may accumulate within vessel 32, ifnecessary.

As described above, systems according to embodiments herein may includea separator 47 configured to separate the two types of catalysts basedon their physical properties, such as particle size and/or density.Separator 47 may be a cyclone separator, a screen separator, mechanicalsifters, a gravity chamber, a centrifugal separator, a baffle chamber, alouver separator, an in-line or pneumatic classifier, or other types ofseparators useful for efficiently separating particles based on sizeand/or hydrodynamic properties.

Examples of separators or classifiers useful in embodiments herein areillustrated in FIGS. 2-5. In some embodiments, separator 47 may be aU-shaped inertial separator, as illustrated in FIG. 2, to separate twokinds of solid particles or catalysts with different particle sizesand/or particle density. The separator may be built in the form ofU-shape, having an inlet 70 at the top, a gas outlet 84 at the other endof the U, and a main solid outlet 80 at the base of U-shaped separator.

A mixture 72 of solid particles or catalysts with different sizes isintroduced along with a carrier gas stream through inlet 70 and inertialseparation forces are applied on the solids by making no more than oneturn to separate the different sizes of solid particles. Larger and/ormore dense solid particles 78 preferentially go downward in sections74/76 to a standpipe or dipleg 80 connected to the base of U-shape whilelighter or smaller solid particles are preferentially carried along withthe gas stream to outlet 82, where the mixture 84 of small particles andgases may be recovered. The solid outlet 80 at the base of U-shapedseparator (the inlet of the standpipe or dipleg used to flow the largerand/or more dense catalyst particles back to the second reactor 32)should be large enough to accommodate the normal solid/catalyst flow.

By controlling the gas flow rates entering the downward standpipe andexiting the main gas stream outlet, the overall separation efficiency ofthe U-shape inertial separator and the selectivity to separate largerand/or more dense particles from smaller and/or less dense particles canbe manipulated. This extends to a fully sealed dipleg where the only gasstream exiting the dipleg are those entrained by the exitingsolid/catalyst flow. As the U-shaped inertial separator provides theability to manipulate the separation efficiency, intermediate sizedparticles, which have the potential to accumulate in the system as notedabove, may be periodically or continuously entrained with thehydrocarbon products recovered from separator 47 for separation invessel 8 and regeneration in regenerator 24.

In some embodiments, a gas sparger 75 or extra steam/inert gas may beprovided proximate a top of outlet section 80, such as near a top of thestandpipe inlet. The additional lift gas provided within the separatormay further facilitate the separation of larger and/or more dense solidparticles from less dense and/or smaller solid particles, as the extragas may preferentially lift lighter solid particles to gas outlet 84,resulting in better solid classification.

The cross sectional area of the U-shaped separator at the inlet 70,outlet 82 and throughout the U-shaped separator (including areas 74, 76)may be adjusted to manipulate the superficial gas velocity within theapparatus to control the separation efficiency and the selectivity. Insome embodiments, a position of one or more of the separator walls maybe adjustable, or a movable baffle may be disposed within one or moresections of the separator, which may be used to control the separationefficiency and selectivity. In some embodiments, the system may includea particle size analyzer downstream of outlet 82, enabling real-timeadjustment of the flow configuration through the U-shaped separator toeffect the desired separations.

Utilization of U-shaped inertial separators connected in series or acombination of U-shape inertial separators and cyclones may provideflexibility to allow simultaneously achievement of both target overallseparation efficiency and target selectivity of larger and/or more denseparticles over smaller and/or less dense particles.

The secondary reactor 32 may also be equipped with baffles or structuredinternals such as modular grids as described in U.S. Pat. No. 7,179,427.Other types of internals that enhance contact efficiency and productselectivity/yields may also be used. The internals may enhance thecatalyst distribution across the reactor and improve the contact of feedvapors with catalyst, leading to an increase in the average reactionrate, enhance the overall activity of the catalyst and optimize theoperating conditions to increase the production of light olefins.

Embodiments disclosed herein use Y-type zeolite or conventional FCCcatalyst, maximizing the conversion of heavy hydrocarbon feeds. TheY-type zeolite or FCC catalyst is of a smaller and/or lighter particlesize than the ZSM-5 or similar catalysts used to enhance the productionof light olefins in the countercurrent flow reactor. The ZSM-5 orsimilar catalysts have a larger particle size and/or are more dense thanthe Y-type zeolite or FCC catalysts used to enhance separations of thecatalyst types in each of the mixed flow reactor and the solidsseparator. The superficial gas velocity of vapors in the second reactoris maintained such that it allows entrainment of the Y-type zeolite orFCC catalyst and a portion of the ZSM-5 or ZSM-11 catalyst out of themixed flow reactor, and the solids separator may utilize the differencesin single particle terminal velocities or differences between minimumfluidization/minimum bubbling velocities to separate and return theZSM-5/ZSM-11 to the mixed flow reactor. This concept allows theelimination of two stage FCC systems and hence a simplified andefficient process. The catalysts employed in the process could be eithera combination of Y-type zeolite/FCC catalyst and ZSM-5 or other similarcatalysts, such as those mentioned in U.S. Pat. Nos. 5,043,522 and5,846,402.

The entrainment of both catalysts from the mixed flow reactor,subsequent separation, and recycle and accumulation of the ZSM-5/ZSM-11catalyst in the mixed flow reactor eliminates any potential restrictionon superficial gas velocity in the secondary reactor. The use of asolids separation vessel thus provides process flexibility in thesecondary reactor, allowing the secondary reactor to be operated inbubbling bed, turbulent bed, or fast fluidization regimes, rather thanrestricting the operations to only a bubbling bed regime. The solidsseparation vessel may be a cyclone or other vessel where solids andgases are introduced at a common inlet, and through degassing, inertialand centrifugal forces, the particles are separated based on size and/ordensity, with the majority of the smaller FCC type particles entrainingwith the vapor outlet, and the larger and/or denser ZSM-5 or ZSM-11 typeparticles returning via a dense phase standpipe or dipleg back to thesecondary reactor vessel 32.

In addition to the U-type particle separator described in relation toFIG. 2, FIGS. 3-5 illustrate various additional particle separationdevices for use in embodiments herein. Referring to FIG. 3, a bafflechamber separator 900 for separating catalysts or other particles basedon size and/or density may include an inlet 910, such as a horizontalconduit. The vapors and particles contained in the horizontal conduitthen enter a chamber 912, before being deflected by a baffle 914. Thechamber 912 is connected to a first vertical outlet 916 and a firsthorizontal outlet 918. The baffle 914 may be located in the middle ofchamber 912, proximate the inlet 910, or proximate the horizontal outlet918 of the chamber. The baffle may be at an angle or moveable such thatthe baffle may be used to deflect more or less catalyst particles, andmay be configured for a particular mixture of particles.

Processes herein may utilize the baffle chamber separator 900 tosegregate larger and/or denser particles from smaller and/or less denseparticles contained in a carrier gas, such as a hydrocarbon reactioneffluent. The baffle chamber separator 900 may be configured to:separate at least a portion of a second particle type from the carriergas and a first particle type, recover the second particle type via thefirst vertical outlet 916 and recover a mixture including the carriergas and the first particle type via the first horizontal outlet 918. Theseparator may also include a distributor (not illustrated) disposedwithin or proximate the first vertical outlet for introducing afluidizing gas, facilitating additional separation of the first particletype from the second particle type.

Referring now to FIG. 4, a louver separator for use in accordance withembodiments herein is illustrated. Similar to other separatorsillustrated and described, the louver separator 1000 may be used forseparating catalysts or other particles based on size and/or density.The louver separator 1000 may include a vertical inlet 1010 connected toa chamber 1012 where one or more vertical sides 1014 of the chamber areequipped with narrow slot outlets 1016, which may be described aslouvers. The number of louvers may vary depending on the application,such as the desired particle mixture to be separated, and the angle ofthe louver may be adjustable in order to control the amount of vaporpassing through and leaving the louver outlets. The chamber 1012 is alsoconnected to a first vertical outlet 1014 at the bottom of the chamber.

Processes herein may utilize the louver separator 1000 to segregatelarger and/or denser particles from smaller and/or less dense particlescontained in a carrier gas, such as a hydrocarbon reaction effluent. Thelouver separator 1000 may be configured to: separate at least a portionof the second particle type from the carrier gas and the first particletype, recover the second particle type via the first vertical outlet1014 and recover the carrier gas and the first particle type via thelouver outlets 1016. The separator may also include a distributor (notillustrated) disposed within or proximate the first vertical outlet forintroducing a fluidizing gas, facilitating additional separation of thefirst particle type from the second particle type.

Referring now to FIG. 5, an inertial separator 1100 for use inaccordance with embodiments herein is illustrated. Similar to otherseparators illustrated and described, the inertial separator 1100 may beused for separating catalysts or other particles based on size and/ordensity. The separator may include an inlet 1110 at the top of andextending into a chamber 1112. In some embodiments, the height ordisposition of inlet 1110 within chamber 1112 may be adjustable. Theseparator may also include one or more side outlets 1114, 1116, such asone to eight side outlets, and a vertical outlet 1118. The separator mayalso include a distributor (not illustrated) disposed within orproximate the vertical outlet 1118 for introducing a fluidizing gas.

A mixture 1172 of solid particles or catalysts with different sizes isintroduced along with a carrier gas stream through inlet 1110. The gasesin the mixture 1172 are preferentially directed toward outlets 1114,1116 based on pressure differentials, and inertial separation forces areapplied on the solids by making the particles and carrier gas turn fromthe extended inlet 1110 within chamber 1112 to flow toward outlets 1114,1116, the inertial forces separating the different sizes/densities ofparticles. Larger and/or heavier solid particles 1174 preferentially godownward in sections 1118 to a standpipe or dipleg (not shown) connectedto the base of the separator, while lighter or smaller solid particles1176 are preferentially carried along with the gas stream to outlets1114, 1116, where the mixture of small particles and gases may berecovered.

In each of the separators described herein, by controlling the gas flowrates entering the downward standpipe/separation chamber and exiting themain gas stream outlet, the overall separation efficiency of theseparator and the selectivity to separate heavier and/or largerparticles from lighter or smaller particles can be manipulated. Thisextends to a fully sealed dipleg where the only gas stream exiting thedipleg are those entrained by the exiting solid/catalyst flow.

In some embodiments, a gas sparger or extra steam/inert gas may beprovided proximate a top of the heavy/dense particle outlet section,such as near a top of the standpipe inlet. The additional lift gasprovided within the separator may further facilitate the separation ofheavier and/or larger solid particles from lighter or smaller solidparticles, as the extra gas may preferentially lift lighter solidparticles to the gas outlets, resulting in better solid classification.

The particle separators described herein may be disposed external orinternal to a vessel. Further, in some embodiments, the large/denseparticle outlets of the particle separators may be fluidly connected toan external vessel, providing for selective recycle or feed of theseparated particles to the desired reactor, so as to maintain a desiredcatalyst balance, for example.

Embodiments disclosed herein, by the methods described above,significantly increase the concentration of desired catalysts in thesecondary reactor (vessel 32), consequently increasing light olefinyield. In addition, this process also serves as a method to decouple thewithdrawal and addition of the ZSM-5 and ZSM5-11 with the withdrawal andaddition of FCC catalyst. In summary, the FCC process presented in thisdisclosure creates a desired ZSM-5 or ZSM-11 catalyst additive richenvironment in the secondary reactor 32, which could preferentiallyconvert light naphtha products, such as those derived from primaryreactor, to improve light olefin yield while simultaneously maximizingmiddle distillate yield by applying optimum operation condition in theprimary reactor or riser.

Another benefit of embodiments disclosed herein is that the integratedtwo-reactor scheme overcomes the heat balance limitations in the standalone C₄/naphtha catalytic cracking processes. The secondary (mixedflow) reactor acts as a heat sink due to integration with the catalystregenerator, minimizing the requirement of catalyst cooler whileprocessing residue feed stocks.

The product vapors from the secondary reactor are transported into thefirst stage reactor/disengaging vessel or reaction termination devicewherein these vapors are mixed and quenched with the products from thefirst stage and or external quench media such as LCO or steam tominimize the unwanted thermal cracking reactions. Alternatively, theproduct outlet line of the secondary reactor/solids separator can alsobe used to introduce additional quantity of heavy feed or re-route partof the feed from the first stage reactor (the riser reactor). Thisserves two purposes: (1) the catalyst in the solids separator vaporoutlet line is predominantly Y-type zeolite/conventional FCC catalystthat is preferred to crack these heavy feed molecules into middledistillates, and (2) such cracking reaction is endothermic that helps inreducing the temperature of the outgoing product vapors and alsoresidence time.

In some embodiments disclosed herein, an existing FCC unit may beretrofitted with a secondary reactor as described above. For example, aproperly sized reactor may be fluidly connected to an existing catalystregeneration vessel to provide catalyst feed and return from the mixedflow vessel, and fluidly connected to an existing disengagement vesselto separate the hydrocarbon products and catalysts. In otherembodiments, a mixed flow reactor may be added to a grass-roots FCC unitthat is aimed at operating in gasoline mode, light olefins mode, ordiesel mode.

The reactor system described above with respect to FIGS. 1 and 6 relatedprimarily to light olefins production, and advantageous concentration ofa catalyst in a mixed catalyst system to enhance reactivity andselectivity of the system. Such a reactor system may also be used forother mixed catalyst systems, where concentration of one of thecatalysts may be advantageous.

For example, in some embodiments, the reaction system may be used forgasoline desulfurization, where catalyst mixture may include a smallerand/or less dense FCC catalyst, such as zeolite Y, and a larger and/ordenser catalyst, such as a gasoline desulfurization additive. Such aprocess is described with respect to FIG. 7.

Referring now to FIG. 7, a simplified process flow diagram of systemsfor cracking and desulfurizing hydrocarbons according to embodimentsdisclosed herein is illustrated. The system includes a two-reactorconfiguration for producing olefins, such as propylene and ethylene,from petroleum feedstocks or other hydrocarbon streams. The firstreactor 3 may be a riser reactor for cracking heavier hydrocarbon feeds,for example. The second reactor 32 is a fluidized bed reactor, which maybe equipped with baffles or internals. The cracked hydrocarbon products,including olefins and/or light naphtha products from the first reactor 3or similar feed streams from external sources, may be processed in thesecond reactor 32 to enhance the quality of the product, such asdecreasing the overall sulfur content of the hydrocarbons processed inthe second reactor.

A heavy petroleum residue feed is injected through one or more feedinjectors 2 located near the bottom of first reactor 3. The heavypetroleum feed contacts hot regenerated catalyst introduced through aJ-bend 1. The catalyst fed to the first reactor 3 is a catalyst mixture,including a first catalyst selective for cracking heavier hydrocarbons,such as a Y-type zeolite based catalyst, and a second catalyst selectivefor the desulfurization of naphtha range hydrocarbons, which may also beused in combination with other catalysts. The first and second catalystsmay be different in one or both particle size and density.

The heat required for vaporization of the feed and/or raising thetemperature of the feed to the desired reactor temperature, such as inthe range from 500° C. to about 700° C., and for the endothermic heat(heat of reaction) may be provided by the hot regenerated catalystcoming from the regenerator 17.

After the major part of the cracking reaction is completed, the mixtureof products, unconverted feed vapors, and spent catalyst flow into a twostage cyclone system housed in cyclone containment vessel 8. Thetwo-stage cyclone system includes a primary cyclone 4, for separatingspent catalyst from vapors. The spent catalyst is discharged intostripper 9 through primary cyclone dip leg 5. Fine catalyst particlesentrained with the separated vapors from primary cyclone 4 and productvapors from second reactor 32, introduced via flow line 36 a and asingle stage cyclone 36 c, are separated in second stage cyclone 6. Thecatalyst mixture collected is discharged into stripper 9 via dip leg 7.The vapors from second stage cyclone 6 are vented through a secondarycyclone outlet 12 b, which may be connected to plenum 11, and are thenrouted to a fractionator/gas plant 410 for recovery of products,including the desired olefins. If necessary, the product vapors arefurther cooled by introducing light cycle oil (LCO) or steam viadistributor line 12 a as a quench media.

The fractionator 410 may be, for example, a main fractionator of an FCCplant, and may produce various hydrocarbon fractions, including a lightolefin-containing fraction 412, a naphtha fraction 414, and a heaviesfraction 416, among other various hydrocarbon cuts. The products routedto fractionator/gas plant 410 may include other light gases, such ashydrogen sulfide that may be produced during desulfurization;Separators, absorbers, or other unit operations may be included wheresuch impurities are desired to be separated upstream of the mainfractionator/gas plant.

The spent catalyst recovered via dip legs 5, 7 undergoes stripping instripper bed 9 to remove interstitial vapors (the hydrocarbon vaporstrapped between catalyst particles) by countercurrent contacting ofsteam, introduced to the bottom of stripper 9 through a steamdistributor 10. The spent catalyst is then transferred to regenerator 17via the spent catalyst standpipe 13 a and lift line 15. Spent catalystslide valve 13 b, located on spent catalyst standpipe 13 a, is used forcontrolling catalyst flow from stripper 9 to regenerator 17. A smallportion of combustion air or nitrogen may be introduced through adistributor 14 to help smooth transfer of spent catalyst.

Coked or spent catalyst is discharged through spent catalyst distributor16 in the center of the dense regenerator bed 24. Combustion air isintroduced by an air distributor 18 located at the bottom of regeneratorbed 24. Coke deposited on the catalyst is then burned off in regenerator17 via reaction with the combustion air. The catalyst fines entrainedalong with flue gas are collected in first stage cyclone 19 and secondstage cyclone 21 and are discharged into the regenerator catalyst bedthrough respective dip legs 20, 22. The flue gas recovered from theoutlet of second stage cyclone 21 is directed to flue gas line 50 viaregenerator plenum 23 for downstream waste heat recovery and/or powerrecovery.

A first part of the regenerated catalyst mixture is withdrawn viaregenerated catalyst standpipe 27, which is in flow communication with Jbend 1. The catalyst flow from regenerator 17 to reactor 3 may beregulated by a slide valve 28 located on regenerated catalyst standpipe27. The opening of slide valve 28 is adjusted to control the catalystflow to maintain a desired top temperature in reactor 3.

In addition to lift steam, a provision is also made to inject feedstreams such as C₄ olefins and naphtha or similar external streams as alift media to J bend 1 through a gas distributor 1 a located at theY-section for enabling smooth transfer of regenerated catalyst from Jbend 1 to reactor 3. J bend 1 may also act as a dense bed reactor forcracking C₄ olefins and naphtha streams into light olefins at conditionsfavorable for such reactions.

A second part of the regenerated catalyst mixture is withdrawn into asecond reactor 32 through a standpipe 30. A valve 31 may be used tocontrol the catalyst flow from regenerator 17 to second reactor 32 basedon a vapor outlet temperature set point. One or more hydrocarbonfractions, such as naphtha streams, may be injected into the bottomsection of the catalyst bed through one or more feed distributors 34 (34a, 34 b), either in liquid or vapor phase. In some embodiments, thenaphtha feed may include a portion or all of the naphtha 414 from thefractionator 410. Second reactor 32 operates in a mixed flow fashion,where a portion of the regenerated catalyst flows downward (from the topto the bottom of the reactor bed) and/or circulates within vessel 32,and a portion of the regenerated catalyst mixture and the feedhydrocarbon stream flows upward (from the bottom to the top of thereactor bed, the smaller/less dense particles carrying out of the top ofthe reactor with the effluent hydrocarbons).

Second reactor 32 may be equipped with baffles or structured internals(not shown) that help intimate contact and mixing of catalyst and feedmolecules. These internals may also help in minimizing channeling,bubble growth, and/or coalescence. Second reactor 32 may also beenlarged at different sections along the length to maintain a constantor desired superficial gas velocity within the sections.

After the reaction is completed, the catalyst is stripped at thebottommost portion of second reactor 32 to separate entrainedhydrocarbon feed/products using steam as a stripping media introducedthrough distributor 35. The spent catalyst recovered at the bottom ofreactor 32 may then be withdrawn through catalyst withdrawal line 418.Alternatively, the spent catalyst recovered at the bottom of reactor 32may be transferred to regenerator 17, as described above with respect toFIG. 1 (via standpipe 37 and lift line 40 through a spent catalystdistributor 41, where combustion air or nitrogen may be introducedthrough distributor 39 to enable smooth transfer of catalyst toregenerator 17). A valve (not illustrated) may be used to control thecatalyst flow from second reactor 32.

As noted above, second reactor 32 utilizes two different catalysts thatmay differ in one or both of particle size and/or density, such as aless dense and/or smaller Y-type zeolite or FCC catalyst and a largerand/or denser desulfurization catalyst. The superficial gas velocity insecond reactor 32 is maintained such that essentially all or a largeportion of the lighter, smaller catalyst and a portion of the largerand/or denser catalyst is carried out of the reactor with thehydrocarbon products and steam recovered via effluent flow line 45. Aportion of the larger and/or denser catalyst may be retained within thereactor 32, forming a dense bed toward the lower portion of the reactor,as noted above.

The effluent from reactor 32 recovered via flow line 45 may thus includedesulfurized hydrocarbon products, unreacted hydrocarbon feedstock,steam (stripping media), and a catalyst mixture, including essentiallyall of the lighter and/or smaller catalyst and a portion of the heavierand/or larger catalyst introduced to reactor 32. The effluent may thenbe transported via flow line 45 to a solids separator 47. Separator 47may be a separator configured to separate the two types of catalystbased on their physical properties, namely particle size and/or density.For example, separator 47 may use differences in inertial forces orcentrifugal forces to separate the smaller and/or lighter catalyst fromthe larger and/or heavier catalyst. The solids separation vessel 47 isan external vessel to the second reactor 32 and is operated athydrodynamic properties that enhance the separation of the two types ofcatalyst based on their physical properties.

After separation in separator 47, the smaller and/or lighter catalyst(Y-type zeolite/FCC catalyst) is then transported from separator 47 tothe common disengager or containment vessel 8, housing the riser reactorcyclones and/or reaction termination system, via outlet line 36 a. Thelarger and/or heavier desulfurization catalyst may be returned via flowline 49 to the mixed flow reactor 32 for continued reaction withhydrocarbon feeds introduced through distributors 34 a/b.

Entrainment of essentially all of the lighter/smaller catalyst and aportion of the heavier and/or larger catalyst, subsequent separations,and recycle of the heavier and/or larger catalyst to reactor 32 mayallow for a significant accumulation of the larger and/or heavierdesulfurization catalyst in reactor 32. As this catalyst is moreselective for the desulfurization of naphtha range hydrocarbons, theaccumulation of the larger and/or heavier catalyst may provide aselectivity and yield advantage. Further, operation of the reactor in afluidization flow regime to entrain both types of catalyst may providefor improved operability of the reactor or flexibility in operations, asdiscussed above.

A hydrocarbon feed such as heavy vacuum gas oil or heavy residue feed,light cycle oil (LCO), or steam may be injected as a quench media in theoutlet line 36 a through a distributor 36 b. The flow rate of suchquench media may be controlled by setting the temperature of the streamentering the containment vessel 8. All the vapors from second reactor32, including those fed through distributor 36 b, are discharged intothe dilute phase of containment vessel 8 through a single stage cyclone36 c. Employing a hydrocarbon feed as a quench media is preferred as itserves dual purpose of cooling the products from second reactor 32 andalso enhances the production of middle distillates.

The first stage reactor 3, such as a riser reactor, may operates in thefast fluidization regime (e.g., at a gas superficial velocity in therange from about 3 to about 10 m/s at the bottom section) and pneumatictransport regime (e.g., at a gas superficial velocity in the range fromabout 10 to about 20 m/s) in the top section.

WHSV in second reactor 32 is typically in the range from about 0.5 toabout 50 h⁻¹; vapor and catalyst residence times may vary from about 2to about 20 seconds. As necessary, make-up catalyst may be introducedvia one or more flow lines 42, 43. For example, fresh or make-up FCC orY-type zeolite catalyst or a mixture of these two may be introduced toregenerator 17 via flow line 42 and fresh or make-up gasolinedesulfurization additive may be introduced to second reactor 32 via flowline 43. Overall system catalyst inventory may be maintained bywithdrawing mixed catalyst from regenerator 24, for example, and/orreactor 32. Catalyst inventory and accumulation of the preferredcatalyst within reactor 32 may be controlled, such as described above.Additionally, in some embodiments, a catalyst hopper 26 may be used inconjunction with catalyst withdrawal line 25, pressure equalization line29, and standpipe 27, as described above.

Similarly, the reactor system of FIG. 7 may be used for advantageousprocessing of heavy hydrocarbon feedstocks, including heavy crudes orvirgin crudes. In such an embodiment, the mixed catalyst system mayinclude, for example, a smaller and/or less dense FCC catalyst, such aszeolite-Y, and a larger and/or denser heavy oil treatment additive. Forexample, the heavy oil treatment additive may be one of an active matrixcatalyst, a metals trapping additive, a coarse and/or dense Ecat(equilibrium catalyst), a matrix or binder type catalyst (such as kaolinor sand) or a high matrix/zeolite ratio FCC catalyst, among others. Theheavy oil treatment additive may have minimal catalytic activity towardscracking of heavier hydrocarbons and may simply supply the surface areanecessary for thermal cracking reactions to take place. The heavyhydrocarbon feed may be introduced to reactor 32 via distributors 43a/b, and the system may be operated as described above to enhance theprocessing of heavy hydrocarbon feedstocks.

WHSV in the second reactor 32 when operating under heavy hydrocarbontreatment conditions is typically in the range from 0.1-100 hr-1; vaporand particle residence times may vary from 1-400 seconds. As necessary,makeup particles may be introduced via one or more lines 42, 43; it maybe advantageous to add the FCC or Y-type catalyst to the regenerator 17via line 42 and the heavy oil treatment additive via line 43 to thesecond reactor 32. Overall system activity is maintained by withdrawingparticles via line 418 from the second reactor 32 and from theregenerator 24. Solids inventory and the accumulation of the preferredheavy oil treatment additive in second reactor 32 may be controlled byadditions through line 43 and withdrawals through line 418. Operatingtemperature in second reactor 32 is controlled using catalyst fromregenerator 17 line 30 via valve 31 and may range from 400-700° C. Insome embodiments, the product of second reactor 32 may be essentiallythe feed for primary riser reactor 3. Additionally, in some embodiments,a catalyst hopper 26 may be used in conjunction with catalyst withdrawalline 25, pressure equalization line 29, and standpipe 27, as describedabove

In general, the process flow diagrams illustrated in FIGS. 1, 6, and 7use the catalyst/particle separation technology to process additional orrecycle hydrocarbon feedstocks in a secondary vessel. The catalystmixture circulating through the system may include catalysts selectiveto particular reactions, such as cracking, desulfurization,demetalization, denitrogenation, and other, where the catalysts of themixture are selected to have differing physical properties, as describedabove, such that a desired catalyst may be concentrated in the secondaryreactor. Regenerated catalyst is fed to the secondary reactor/vesselwhich may operate in fast fluidized, bubbling, or turbulent bedoperation (depending on application). The effluent of the secondaryreactor/vessel goes to the separator 47, where the primary and secondarycatalysts are separated based on size and/or density and the separatorbottoms, which is enriched in the secondary catalyst, is recycled backto the secondary reactor/vessel. The secondary reactor/vessel hasoptional catalyst withdrawals which may be advantageous depending onapplication as well as different hydrocarbon feeds depending onapplication. The concentration of the secondary catalyst may enhance theoperability, flexibility, and selectivity of the overall reactionsystem.

The separator 47 as described above with respect to FIG. 2 may be usedto enhance productivity and flexibility of mixed catalyst hydrocarbonprocessing systems, where the separator 47 may be located at otheradvantageous locations within the system. Such processes and systems aredescribed further below with respect to FIGS. 8-11, where like numeralsrepresent like parts.

Referring now to FIG. 8A, a simplified process flow diagram of systemsfor converting hydrocarbons and producing olefins according toembodiments disclosed herein is illustrated, where like numeralsrepresent like parts. The process scheme of FIG. 8A adds a catalystholding vessel 510 which is fed regenerated catalyst from the FCCregenerator via catalyst withdrawal line 30 and valve 31. The holdingvessel 510 may be fluidized with a fluidization medium, such as air,nitrogen, or steam, for example, introduced via flow line 516. Theholding vessel effluent 45 is sent to the separator 47 where the mixtureof catalysts is separated. The separator bottoms 49, which is enrichedin the larger and/or heavier catalyst, is recycled back to catalystholding vessel 510, where the concentration of the larger and/or densercatalyst will build up. The remaining stream 514 from the separator 510is returned to the disengagement vessel 8 in this embodiment. Thebottoms 512 of the holding vessel may be coupled to a slide valve (notillustrated) which can control the feed of catalyst to secondaryreactor/vessel 32, which can be operated in a similar fashion to thatdescribed above with respect to FIGS. 1, 6, and 7. Advantageously, thecatalyst concentrated in vessel 510 will not be saturated withhydrocarbon and may allow for lower contact times with catalyst in thesecondary reactor/vessel 32.

FIG. 8B illustrates a system similar to that of FIG. 8A, except thecatalyst recovered from separator 47 via flow line 514 is returned tothe catalyst regenerator 17 as opposed to being forwarded to thedisengagement vessel 8. The vessel to which the catalyst in flow line514 is forwarded may depend upon the type of fluidization gas introducedvia flow line 516 as well as the capabilities of the systems receivingflow from either regenerator 17 or vessel 8, via flow lines 50 and 12 b,respectively. Where the fluidization gas is steam, for example, thecatalyst in flow line 514 is preferably forwarded to vessel 8; where thefluidization gas is air or nitrogen, for example, the catalyst in flowline 514 is preferably forwarded to regenerator 17.

FIGS. 8A and 8B illustrate the smaller particles recovered via flow line514 as being forwarded to the regenerator 17 or disengagement vessel 8,and the larger and/or heavier particles recovered via flow line 512 asbeing forwarded to secondary reactor 32. Embodiments herein alsocontemplate forwarding of the smaller and/or lighter particles recoveredvia the separator 47 and flow line 514 to secondary reactor 32 whilerecirculating the larger and/or heavier particles to the regenerator 17or stripper 9.

FIGS. 8A and 8B further illustrate a system with a vessel 510accumulating/concentrating large particles for use in the secondaryreactor. Where a single-pass separation may suffice, the containmentvessel 510 may be excluded from the system, as illustrated in FIGS. 9Aand 9B, where like numerals represent like parts. In these embodiments,the catalyst mixture is fed directly from the catalyst regenerator 17via dip leg 30 to separator 47. Air or other fluidization gases may besupplied via flow line 610, provided at a flow rate sufficient for theinertial separations. The smaller/lighter particles may be recovered viaflow line 612 and the larger and/or heavier particles may be recoveredvia flow line 614. FIG. 9A illustrates the larger and/or heavierparticles being forwarded to secondary reactor 32, whereas FIG. 9Billustrates the smaller and/or lighter particles being forwarded tosecondary reactor 32.

FIGS. 9A and 9B illustrate return of a particle portion to theregenerator 17. Similar to the above description with respect to FIGS.8A and 8B, the particles not fed to reactor 32 may be returned to eitherthe regenerator 17 or the disengagement vessel 8, and such may depend onthe fluidization medium and/or downstream processing capabilities.

The process schemes illustrated in FIGS. 9A and 9B use a single passversion of the separator as opposed to those versions that incorporaterecycle to increase the concentration. In this scheme, the regeneratedcatalyst is directed to the separator where either the bottoms oroverhead of the separator can be directed to the secondary reactor. Ifthe bottoms were to be directed, the catalyst would be enriched based onthe larger and/or denser particles. If the overhead of the separatorwere to be directed to the secondary reactor, the catalyst would beenriched in the smaller and/or less dense particles. This scheme couldalso be arranged such that no secondary reactor is present, and theseparator is between the regenerator and the primary riser reactor,concentrating a catalyst similar to that described for the process ofFIG. 11, below.

The embodiments of FIGS. 8A/B decouple the recycle catalyst from thesecondary reactor, achieving a higher concentration of the desiredcatalyst in the secondary reactor, however requiring additional capitalcosts. The embodiments of 6A/B also decouple the recycle catalyst fromthe secondary reactor, achieving a moderate increase in concentration ofthe desired catalyst as compared to the flow scheme of FIG. 7, forexample, but at a lower capital cost than the embodiment of FIGS. 9A/B.

Referring now to FIG. 10, a simplified process flow diagram of systemsfor processing hydrocarbons according to embodiments disclosed herein isillustrated, where like numerals represent like parts. This processschemes removes the secondary reactor and has the separator 47 receivingan effluent from the primary riser 3. The riser effluent, which containsa mixed catalyst, could be directed to the separator 47 where a portionof catalyst is recycled to the riser 3 from the separator bottoms 710,thereby enriching the concentration of the larger and/or heaviercatalyst in the riser reactor 3. The overhead 712 of the separator 47would continue to the stripper vessel 8, where the hydrocarbon productswould be separated from the remaining catalyst. This configuration couldalso be used with a catalyst mixture with no degree of classification asa method of recycling spent catalyst to the riser 3.

The enriched catalyst fraction 710 may be introduced to the riser 3upstream or downstream (as illustrated) of the regenerated catalyst feedinlet from standpipe 27, and in some embodiments may be introduced atone or more points along the length of the riser reactor 3. The inletpoint may be based on secondary hydrocarbon feeds, temperature of therecirculating catalyst 710, and other variables that may be used toadvantageously process hydrocarbons in the riser reactor 3.

The hydrocarbon products recovered from disengagement vessel 8/stripper9 may be forwarded, as described above, to a fractionator/gas plant 720,for separation and recovery of one or more hydrocarbon fractions 722,724, 726, 728, 730. One or more of the recovered hydrocarbon fractionsfrom the fractionator/gas plant in embodiments herein may berecirculated to the riser reactor 3 or secondary reactor 32 for furtherprocessing.

a simplified process flow diagram of systems for processing hydrocarbonsaccording to embodiments disclosed herein is illustrated, where likenumerals represent like parts. In this process scheme, a regeneratorcatalyst hopper 26 is fluidly connected to riser reactor 3. Regeneratedmixed catalyst, which contains a smaller and/or less dense catalyst anda larger and/or denser catalyst, flows from the regenerator 17 to theregen catalyst hopper 26. The hopper 26 is fluidized with steam and/orair, provided by distributor 810. The overhead effluent 816 of thehopper flows to the separator 47. In the separator 47, which is aseparation device as described previously, the catalysts are separated,and the bottoms 814, which is enriched in the larger and/or densercatalyst, may be fed back to the regen catalyst hopper 26, such as whenfluidized with air, or to disengagement vessel 8, such as when fluidizedwith steam. This will increase the concentration of the larger and/ordenser catalyst in the regen catalyst hopper 26. The overhead 812 of theseparator 47 may be directed to either the regenerator or the strippervessel. The bottom 27 of the regenerator catalyst hopper has awithdrawal with slide valve 28 which controls the flow of catalyst whichis enriched in the larger and/or denser catalyst to the riser 3. In thismanner, the riser 3 operates with an effective higher concentration ofcatalyst than the inventory in the system, creating preferentialproducts based on the properties of the catalyst.

Concentration of a catalyst in the regen catalyst hopper as describedabove with respect to FIG. 11 may be performed intermittently. Thesystem may circulate the catalyst mixture through the riser, stripper,and regenerator, without sufficient fluidization in the hopper 26 toentrain catalysts to the separator 47. When there is a change in thedesired product mixture, the hydrocarbon feeds, or other factors, whereit may be advantageous to operate with a higher concentration of aparticular catalyst in the catalyst mixture, the catalyst in the regenhopper 26 may be fluidized and separated using separator 47. Whenfactors again change, fluidization of the catalyst hopper may bediscontinued. In this manner, the flexibility of the system with regardto products and feed may be enhanced.

While FIGS. 10 and 11 are illustrated with a single riser, the solidsseparation device may be used to enhance the performance of a multipleriser system. For example, a two-riser system may benefit from theconcentration of one catalyst in a riser, which may be processingdifferent feeds than a second riser.

Embodiments herein may utilize various types of catalysts or particlesto perform desired reactions, where a common regenerator may be used toregenerate the mixture of catalysts, and a separator is advantageouslylocated to enrich one or more reactors with a particular catalystcontained in the mixture of catalysts. Embodiments herein may be used toimprove unit operations, and enhance the selectivity and flexibility ofthe reaction systems, such as for applications including light olefinsproduction, gasoline desulfurization, and heavy oil processing.

Light olefins production may include various light, medium, and heavyhydrocarbon feeds to the riser, as described above. Feeds to the secondreactor 32 may include naphtha, such as straight run naphtha or recyclecat naphtha, among other feeds. The catalyst mixture for light olefinsproduction may include a smaller and/or less dense catalyst, such as anFCC catalyst (zeolite Y, for example), and a heavier/denser catalyst,such as ZSM-5 or ZSM-11, among other combinations. Other crackingcatalysts may also be used Various catalysts for the cracking ofhydrocarbons are disclosed in U.S. Pat. Nos. 7,375,257, 7,314,963,7,268,265, 7,087,155, 6,358,486, 6,930,219, 6,809,055, 5,972,205,5,702,589, 5,637,207, 5,534,135, and 5,314,610, among others.

Embodiments directed toward gasoline desulfurization may include variouslight, medium, and heavy hydrocarbon feeds to the riser, as describedabove. Feeds to the second reactor 32 may also include naphtha, such asstraight run naphtha or recycle cat naphtha, among other feeds. Thecatalyst mixture for light olefins production may include a smallerand/or less dense catalyst, such as an FCC catalyst (zeolite Y, forexample), and a larger and/or denser catalyst, with desulfurizationfunctionality such as a MgO/Al₂O₃ with various metals promotion. Otherdesulfurization catalysts may also be used as disclosed in U.S. Pat.Nos. 5,482,617, 6,482,315, 6,852,214, 7,347,929 among others. In someembodiments, the catalyst mixture may include a cracking catalystcomposition having desulfurization activity, such as those disclosed inU.S. Pat. No. 5,376,608, among others.

Embodiments directed toward heavy oil processing may include variouslight, medium, and heavy hydrocarbon feeds to the riser, as describedabove. Feeds to the second reactor 32 may include hydrocarbons orhydrocarbon mixtures having boiling points or a boiling range aboveabout 340° C. Hydrocarbon feedstocks that may be used with processesdisclosed herein may include various refinery and other hydrocarbonstreams such as petroleum atmospheric or vacuum residua, deasphaltedoils, deasphalter pitch, hydrocracked atmospheric tower or vacuum towerbottoms, straight run vacuum gas oils, hydrocracked vacuum gas oils,fluid catalytically cracked (FCC) slurry oils, vacuum gas oils from anebullated bed hydrocracking process, shale-derived oils, coal-derivedoils, tar sands bitumen, tall oils, bio-derived crude oils, black oils,as well as other similar hydrocarbon streams, or a combination of these,each of which may be straight run, process derived, hydrocracked,partially desulfurized, and/or partially demetallized streams. In someembodiments, residuum hydrocarbon fractions may include hydrocarbonshaving a normal boiling point of at least 480° C., at least 524° C., orat least 565° C. The catalyst mixture for heavy hydrocarbon processingmay include a smaller and/or less dense catalyst, such as an FCCcatalyst (zeolite Y, for example), and a larger and/or denser catalyst,such as an active matrix catalyst, a metals trapping catalyst, acoarse/dense Ecat (equilibrium catalyst), a matrix or binder typecatalyst (such as kaolin or sand) or a high matrix/zeolite FCC catalyst.Other cracking catalysts may also be used, such as, for example, one ormore of those disclosed in U.S. Pat. Nos. 5,160,601, 5,071,806,5,001,097, 4,624,773, 4,536,281, 4,431,749, 6,656,347, 6,916,757,6,943,132, and 7,591,939, among others.

Systems herein may also be utilized for pre-treatment of a heavy crudeor virgin crude, such as a crude oil or bitumen recovered from tarsands. For example, reactor 32, such as that in FIG. 1 or 9, amongothers, may be used to pre-treat the bitumen, prior to furtherprocessing of the treated heavy crude in downstream operations, whichmay include separation in a downstream separation system and recycle ofone or more fractions for further conversion in reactor 3. The abilityto pre-treat the heavy crude with a preferred particle within a particleor catalyst mixture may advantageously allow integration of heavy crudeprocessing where it otherwise would be detrimental to catalyst andoverall system performance.

Embodiments herein describe the catalyst mixture being separated by theseparator and the effective preferential concentration of a catalystwithin the mixture in a reactor. As illustrated in the Figures, thecatalyst being concentrated in the reactor is illustrated as beingreturned from the separator proximate the top of the reactor or vessel.Embodiments herein also contemplate return of the catalyst from theseparator to a middle or lower portion of the reactor, and where thecatalyst is returned may depend on the hydrocarbon feeds beingprocessed, the catalyst types in the mixture, and the desired catalystgradient within the reactor vessel. Embodiments herein also contemplatereturn of the catalyst to multiple locations within the reactor. Whileproviding the ability to enhance the concentration of a particularcatalyst or particle within a mixture in a given reactor, embodimentsherein may also be used for a one catalyst system; the particleseparators and systems described herein may increase the catalyst/oilratio, which enhances catalytic contact time

As described for embodiments above, a second reactor is integrated witha FCC riser reactor and separation system. This reactor is in flowcommunication with other vessels, allowing selective catalyticprocessing and integrated hydrocarbon product quenching, separation andcatalyst regeneration. Such an integrated reactor system offers one ormore of the above advantages and features of embodiments of theprocesses disclosed herein may provide for an improved or optimalprocess for the catalytic cracking of hydrocarbons for light olefinproduction.

Embodiments herein may employ two types of catalyst particles, such asY-zeolite/FCC catalyst of smaller particle size and/or less density andZSM-5 particles larger in size and/or denser than the former. Aseparator with selective recycle may be utilized to preferentiallysegregate the Y-zeolite from ZSM-5 catalyst. Use of such catalyst systemallows entrainment of lighter and smaller particles, thereby retainingZSM-5 type particles within the additional new reactor bed. Thereactants undergo selective catalytic cracking in presence of ZSM-5 typecatalyst that is preferred to maximize the yield of light olefins fromC₄ and naphtha feed streams. The separator is a device which canfacilitate the separation of two types of catalysts due to thedifference in their particle size and/or density. Examples of separatorswith selective recycle may be a cyclone separator, a screen separator,mechanical sifters, a gravity chamber, a centrifugal separator, anin-line or pneumatic classifier, or other types of separators useful forefficiently separating particles based on size and/or hydrodynamicproperties. The separator is connected to the top of the second reactorwhich is in flow communication with second reactor as well asregenerator and first reactor/stripper.

The reactor may be provided with baffles or modular grid internals. Thisprovides intimate contact of catalyst with hydrocarbon feed molecules,helps in bubble breakage and avoiding bubble growth due to coalescence,channeling or bypassing of either catalyst or feed.

Conventionally, fresh catalyst make-up for maintaining the catalystactivity is introduced to the regenerator bed using plant air. Incontrast, it is proposed to inject the desired high concentrationcatalyst/additive directly into the second reactor bed using steam ornitrogen as conveying media. This helps to produce incremental increasesin concentration and favorable selectivity.

The reactor configurations described herein provide enough flexibilityand operating window to adjust operating conditions such as weighthourly space velocity (WHSV), catalyst and hydrocarbon vapor residencetime, reaction temperature, catalyst/oil ratio, etc. As for example, insome embodiments, the second reactor top/bed temperature is controlledby adjusting catalyst flow from regenerator which indirectly controlsthe catalyst/oil ratio. Whereas reactor bed level may be controlled bymanipulating the spent catalyst flow from reactor to regenerator, whichcontrols the WHSV and catalyst residence time.

While the disclosure includes a limited number of embodiments, thoseskilled in the art, having benefit of this disclosure, will appreciatethat other embodiments may be devised which do not depart from the scopeof the present disclosure. Accordingly, the scope should be limited onlyby the attached claims.

What is claimed:
 1. A particle separator for separating catalysts orother particles based on size and/or density, comprising: an inlet forproviding a mixture comprising a carrier gas, a first particle type, anda second particle type, each particle type having a particle sizedistribution, an average particle size and an average density, thesecond particle type having an average particle size and/or averagedensity greater than the first particle type; a chamber for receivingthe mixture, wherein the chamber is configured to separate at least aportion of the second particle type from the carrier gas and the firstparticle type; a first outlet to recover the second particle type; asecond outlet to recover the carrier gas and the first particle type;and a distributor disposed within or proximate the first outlet forintroducing a fluidizing gas, facilitating additional separation of thefirst particle type from the second particle type; wherein across-sectional area of the chamber or a portion thereof is adjustable.2. The separator of claim 1, further comprising a movable baffledisposed within one or more sections of the chamber.
 3. A system for theconversion of hydrocarbons, comprising: a catalyst regenerator; a firstcatalyst feed line for withdrawing a mixture comprising a first catalystand a second catalyst from the catalyst regenerator and feeding themixture to a riser reactor, wherein the first catalyst has a smalleraverage particle size and/or is less dense than the second catalyst; asecond catalyst feed line for withdrawing the mixture comprising a firstcatalyst and a second catalyst from the catalyst regenerator and feedingthe mixture to a catalyst separation system wherein the catalystseparation system comprises: an inlet for providing a mixture comprisingthe fluidization medium, the first catalyst, and the second catalyst; achamber for receiving the mixture, wherein the chamber is configured toseparate at least a portion of the second catalyst from the fluidizationmedium and the first catalyst; a first outlet to recover the secondcatalyst; a second outlet to recover the fluidization medium and thefirst catalyst; and a distributor disposed within or proximate the firstoutlet for introducing a fluidizing gas, facilitating additionalseparation of the first catalyst from the second catalyst; afluidization medium feed line for fluidizing the mixture withdrawn viathe second catalyst feed line with a fluidization medium and separatingthe first catalyst from the second catalyst in the catalyst separationsystem to recover a first stream comprising the first catalyst and thefluidization medium and a second stream comprising the second catalyst;a reactor for contacting a hydrocarbon feedstock and either the firststream or the second stream to react at least a portion of thehydrocarbon to produce a converted hydrocarbon.
 4. The system of claim3, further comprising a feed line for feeding the first stream to thereactor.
 5. The system of claim 3, further comprising a feed line forfeeding the second stream to the reactor.
 6. The system of claim 4,wherein a cross-sectional area of the chamber or a portion thereof isadjustable.
 7. The system of claim 4, further comprising a movablebaffle disposed within one or more sections of the chamber.
 8. A systemfor the conversion of hydrocarbons, comprising: a riser reactor forcontacting a hydrocarbon feedstock with a catalyst mixture comprising afirst catalyst and a second catalyst, wherein the first catalyst has asmaller average particle size and/or is less dense than the secondcatalyst; a catalyst separation system for separating an effluent fromthe riser reactor to recover a first stream comprising the firstcatalyst and converted hydrocarbon feedstock and a second streamcomprising the second catalyst, wherein the catalyst separation systemcomprises an inlet for providing the effluent from the riser reactor,the effluent comprising a mixture of the converted hydrocarbonfeedstock, the first catalyst, and the second catalyst; a chamber forreceiving the mixture, wherein the chamber is configured to separate atleast a portion of the second catalyst from the converted hydrocarbonfeedstock and the first catalyst; a first outlet to recover the secondcatalyst; a second outlet to recover the converted hydrocarbon feedstockand the first catalyst; and a distributor disposed within or proximatethe first outlet for introducing a fluidizing gas, facilitatingadditional separation of the first catalyst from the second catalyst; aflow line for feeding the second stream to the riser reactor.
 9. Thesystem of claim 8, wherein a cross-sectional area of the chamber or aportion thereof is adjustable.
 10. The system of claim 8, furthercomprising a movable baffle disposed within one or more sections of thechamber.
 11. A system for the conversion of hydrocarbons, comprising: acatalyst withdrawal line for withdrawing a mixture comprising a firstcatalyst and a second catalyst from a catalyst regenerator and feedingthe mixture to a catalyst feed/separation system, wherein the firstcatalyst has a smaller average particle size and/or is less dense thanthe second catalyst; the catalyst feed/separation system for separatingthe first catalyst from the second catalyst in the catalystfeed/separation system to produce a first stream comprising the firstcatalyst and a second stream comprising the second catalyst, wherein thecatalyst feed/separation system comprises: an inlet for providing amixture comprising the first catalyst and the second catalyst; a chamberfor receiving the mixture, wherein the chamber is configured to separateat least a portion of the second catalyst from the first catalyst; afirst outlet to recover the second catalyst; a second outlet to recoverthe fluidization medium and the first catalyst; and a distributordisposed within or proximate the first outlet for introducing afluidizing gas, facilitating separation of the first catalyst from thesecond catalyst; a riser reactor for contacting a hydrocarbon feedstockand either the first stream or the second stream to react at least aportion of the hydrocarbon to produce a converted hydrocarbon.
 12. Thesystem of claim 11, wherein a cross-sectional area of the chamber or aportion thereof is adjustable.
 13. The system of claim 11, furthercomprising a movable baffle disposed within one or more sections of thechamber.